Fix recently added enum value type prediction (#10057)
In #9443, some code was added to predict the type of enum values where
it is not explicitly when all enum members have the same type.
However, it didn't consider that subclasses of Enum that have a custom
__new__ implementation may use any type for the enum value (typically it
would use only one of their parameters instead of a whole tuple that is
specified in the definition of the member). Fix this by avoiding to
guess the enum value type in classes that implement __new__.
In addition, the added code was buggy in that it didn't only consider
class attributes as enum members, but also instance attributes assigned
to self.* in __init__. Fix this by ignoring implicit nodes when checking
the enum members.
Fixes #10000.
Co-authored-by: Kevin Wolf <mail@kevin-wolf.de>
